1. Field of the Invention
The present invention relates to an imaging element having a layered structure and an imaging apparatus having the imaging element and, more particularly, to an imaging element having such a construction that an evaluation value for photometry, distance measurement, and the like are detected in accordance with image data.
2. Description of the Related Art
In the related arts, when obtaining position information of an object which is used in focus control in an imaging apparatus, the position information is obtained on the basis of an image signal which is output from an imaging element. There is also used a method whereby an optical signal from an object is directly input to a dedicated detecting apparatus and position information is obtained on the basis of a phase difference in an image shown by the optical signal. In the case of obtaining position information on the basis of image data, since the dedicated detecting apparatus is unnecessary, the imaging apparatus can be miniaturized.
FIG. 16 is a diagram for describing timing for the autofocus image pickup operation (AF evaluation image pickup) at the time of a live view in the imaging apparatus in the related arts. As illustrated in the diagram, in the imaging apparatus in the related arts, image pickup timing is specified by a vertical sync signal (Vertical Driving Pulse: VD). When an AF control signal is turned on, an image for AF evaluation is picked up in response to the VD after a live view image pickup period. When the AF control signal is turned off, the apparatus enters the live view image pickup period again.
As mentioned above, since the live view image pickup period for obtaining the image for live view and the AF operation period for obtaining the image for AF evaluation are serially arranged along a time base, the image for live view and the image for AF evaluation are not simultaneously picked up. Therefore, as illustrated in the diagram, since the image for AF evaluation is picked up for the AF operation period locating between the image pickup periods (frames) of the image for live view, a time lag exists between the image for live view and the image for AF evaluation.
In addition, although the live view display is performed even when the image for AF evaluation is picked up, at this time, the live view display is performed on the basis of the image for AF evaluation. As illustrated in FIG. 7, when the image for AF evaluation is picked up, since a frame rate is set to be higher than the live view image pickup period, a thinning-out rate in the read-out of the imaging element is high and a deterioration in image quality cannot be avoided.
In order to avoid such a drawback, for example, there is a construction in which a pixel for focus signal detection is provided in a pixel portion of the imaging element separately from a pixel for an image pickup signal. According to such a construction, the apparatus has not only a read-out mode for live view in which the signal for image pickup for a live view display is read out but also a read-out mode for focus detection and auto exposure (AE) in which the signal for focus detection and the signal for image pickup to be used for photometry information for auto exposure are read out of the imaging element. Such read-out modes are circulatively and repetitively performed every frame (refer to Japanese Patent Application Laid-Open No. 2009-89105).
However, in Japanese Patent Application Laid-Open No. 2009-89105, since the image signal (that is, charges) is read out from the imaging element on a pixel unit basis, not only it takes a time to transfer the charges but also a transfer data amount increases, thereby increasing electric power consumption. Further, since the image signal serving as an output of the imaging element is processed by another control apparatus or the like, if the transfer data amount is large, a processing burden in the control apparatus increases. In addition, in Japanese Patent Application Laid-Open No. 2009-89105, since the pixel for focus signal detection is provided in the pixel portion, an area of the pixel for the image pickup signal is eventually reduced and the pixel for focus signal detection is not used when obtaining the image pickup signal (image signal), so that the image quality deteriorates.